1. Field of the Invention
The present disclosure relates to a developing device and a process cartridge used in, for example, an electrophotographic type image forming apparatus or an electrostatic recording type image forming apparatus.
2. Description of the Related Art
An image forming apparatus, such as a printer using an electrophotographic process, uniformly charges an electrophotographic photosensitive member (hereinafter, simply referred to as a “photosensitive member”) serving as an image carrying member. Then, the charged photosensitive member is selectively exposed to form an electrostatic image on the photosensitive member. Then, the electrostatic image formed on the photosensitive member is visualized as a toner image by toner which is a developer. Then, the toner image formed on the photosensitive member is transferred to a recording material, such as a recording sheet or a plastic sheet and heat or pressure is applied to the toner image transferred to the recording material to fix the toner image to the recording material. In this way, image recording is performed.
In general, in the image forming apparatus, it is necessary to supply a developer or maintain various kinds of process means. In order to facilitate the supply of the developer or the maintenance of various kinds of process means, for example, a technique has been put to practical use in which the photosensitive member, the charging unit, the developing unit, and the cleaning unit are arranged in a frame to form a process cartridge which is detachably attachable to an image forming apparatus body. According to the process cartridge type, it is possible to provide an image forming apparatus with high usability.
In the image forming apparatus, in some cases, a developing blade is used in the developing device (developing means) in order to regulate the thickness of a layer of the developer (toner) held in the developer carrying member (developing roller) to a predetermined thickness. The developing blade contacts the developing roller to triboelectrically charge toner and forms a toner layer with a predetermined thickness on the developing roller.
Next, a method of bringing the developing blade into contact with the developing roller will be described. There are two kinds of contact methods, that is, a so-called edge contact method of bringing the leading edge of the developing blade into contact with the developing roller and a so-called belly contact method of bringing the plane of the developing blade into contact with the developing roller.
However, in recent years, there is a demand for a reduction in power consumption in a fixing process with a reduction in the energy consumption of an apparatus. In order to reduce power consumption in the fixing process, it is effective to reduce the heat quantity required to melt toner, that is, the melting point of toner. However, the toner with a low melting point is easy to fix at a low temperature, but has low resistance to toner stress (load). When toner passes through the blade, heat or mechanical stress is applied to the toner. Therefore, when the toner with a low melting point is used for a long time, the adhesion of the toner is reduced. In order to solve the problem, in some cases, an external additive, such as mixed silica, is incorporated into toner. In addition, in some cases, wax in the toner bleeds to the surface, which increases the adhesion of toner. As a result, so-called developing blade melt-adhesion in which toner is attached to the toner is likely to occur. When the developing blade melt-adhesion occurs, the toner layer is not stably formed on the developing roller and a so-called “white stripe” is generated in the image. As a result, image quality is likely to be reduced.
When the above-mentioned developing blade comes into contact with the developing roller in the belly contact manner, a toner intake port is formed in front of a contact nip portion (contact region) between the developing roller and the blade, that is, on the upstream side of the contact nip portion in the rotation direction of the developing roller. Contact pressure between the developing blade and the developing roller is not generated in the toner intake port. Therefore, in general, even when toner is attached to the developing blade, it is possible to remove the attached toner using the flowing of toner in the toner intake port. However, when toner with a low melting point is used, the adhesion of the toner increases. Therefore, it is difficult to remove the toner attached to the developing blade using only the flowing of toner in the toner intake portion.
As a result, in the structure in which the developing blade comes into contact with the developing roller in the belly contact manner, the developing blade melt-adhesion is likely to occur on the upstream side of the contact nip portion between the developing roller and the developing blade in the rotation direction of the developing roller.
In order to solve the above-mentioned problems, it is preferable to use the edge contact method of bringing the leading edge of the developing blade into contact with the developing roller. In the related art, various methods and apparatuses have been proposed in order to bring the leading edge of the developing blade into contact with the developing roller.
For example, FIGS. 14 to 16 schematically show a portion of a developing device including the developing blade according to the related art.
Japanese Patent Application Laid-Open No. 09-062096 discloses a developing device with the structure shown in FIG. 14. In the developing device shown in FIG. 14, one end of a thin elastic member 221a is supported in a cantilever manner and an opposing portion, which is the other end, comes into contact with a developing roller 217. That is, the cantilever-supported thin elastic member 221a is a leaf spring with a free length X and is provided with bending by a distance Y to ensure the contact pressure of the thin elastic member 221a with the developing roller 217.
In addition, Japanese Patent Application Laid-Open No. 09-062096 discloses a developing device with the structure shown in FIG. 15. In the developing device shown in FIG. 15, a developing blade 321 which has a thickness of 2 mm to 4 mm and is made of a resin or a metal material with relative high hardness is attached to a blade guide through a coil spring 324 so as to be movable forward and backward. The developing blade 321 comes into pressure contact with a developing roller 317 which is rotated by the force of the coil spring 324 at predetermined pressure.
Japanese Patent Application Laid-Open No. 10-239991 discloses a developing device with the structure shown in FIG. 16. In the developing device shown in FIG. 16, one end of a plate-shaped member 421a has a curved surface. The other end of the plate-shaped member 421a is rotatably supported by a developing container through a fulcrum shaft 423. In addition, the plate-shaped member 421a is urged by a spring 424 to bring the curved surface of the plate-shaped member 421a into contact with the circumferential surface of the developing roller 417.
However, in the above-mentioned related art, it is difficult to prevent the developing blade melt-adhesion on the downstream side of the contact nip portion between the developing roller and the developing blade in the rotation direction of the developing roller. In addition, the related art has the problems to be solved.
In the developing device shown in FIG. 14, a predetermined amount of bending is set to the cantilever-supported thin elastic member 221a, which is a leaf spring, and the thin elastic member 221a is fixed to the developing container to ensure contact pressure with respect to the developing roller 217. Therefore, the leading edge and the ventral surface of the thin elastic member 221a need to contact the developing roller 217 at the same time. In this case, in a pressure distribution in the contact nip (contact region) between the thin elastic member 221a and the developing roller 227, contact pressure is low in a ventral surface portion on the downstream side of the contact nip portion in the rotation direction of the developing roller.
In a region with low contact pressure, toner or an external toner additive tends to stay. When there is a wide region with low contact pressure, it is difficult to remove the toner attached to the thin elastic member 221a. As a result, toner is melted and adhered to the developing blade on the downstream side of the contact nip portion between the developing roller 217 and thin elastic member 221a in the rotation direction of the developing roller.
However, a small amount of bending may be set to the thin elastic member 221a and the thin elastic member 221a may be fixed to the developing container such that only the vicinity of the leading edge of the thin elastic member 221a comes into contact with the developing roller 217. However, in this case, the amount of bending of the thin elastic member 221a is small. As a result, the contact pressure between the thin elastic member 221a and the developing roller 217 is unstable due to, for example, a variation in the dimensions or set position of the developing blade and the variation of the circumference of the developing roller 217 (a variation in the radius of the developing roller in the circumferential direction). Therefore, high-accuracy assembly is needed in order to set stable contact pressure.
In the developing device shown in FIG. 15, the gap of the developing blade 321 with respect to a blade guide occurs, which is a structural problem. Therefore, the developing blade 321 is inclined in the rotation direction of the developing roller 317 by frictional force in the contact portion between the developing blade 321 and the developing roller 317 and it is difficult to maintain a predetermined position. As a result, it is difficult to stably regulate a predetermined amount of toner on the developing roller 317.
In the developing device shown in FIG. 16, the plate-shaped member 421a has the curved surface and the curved surface comes into contact with the circumferential surface of the developing roller 417. In addition, the size of the toner intake port is increased by the curved surface. Therefore, the melt-adhesion of toner is likely to occur in the plate-shaped member 421a on the upstream side of the contact nip portion between the developing roller 417 and the plate-shaped member 421a in the rotation direction of the developing roller. When the curved surface comes into contact with the circumferential surface of the developing roller 417, a wide region with low contact pressure is formed on the downstream side of the contact nip portion in the rotation direction of the developing roller, in the pressure distribution in the contact nip portion. Therefore, the adhesion of toner is likely to occur in the developing blade on the downstream side of the contact nip portion between the developing roller 417 and the developing blade in the rotation direction of the developing roller.
When the size of the toner intake portion increases, the developing blade is lifted up by toner which flows into the intake port by the wedge effect. Therefore, the load required for regulation needs to increase in order to coat a thin toner layer. When the load applied from the developing blade to the developing roller 417 increases, mechanical stress applied to toner also increases. As a result, toner is likely to deteriorate and the adhesion of the toner increases. Therefore, toner is likely to be melted and adhered to the developing blade.